1. Field of the Invention
The present invention relates to a waveguide-to-microstrip transition mainly used in a microwave band and a millimeter-wave band.
2. Description of the Background Art
In a conventional waveguide-to-microstrip transition, a dielectric substrate is fixed so as to be held between a waveguide and a shorting waveguide block. A strip conductor pattern is provided on one surface of the dielectric substrate, and a ground conductor pattern connected to an opening portion of the waveguide is provided on the other surface of the dielectric substrate. The strip conductor pattern, the ground conductor pattern, and the dielectric substrate constitute a microstrip line. If a distance between a shorting surface of the shorting waveguide block and the strip conductor pattern is set to about ¼ of a guide wavelength of the waveguide, then a magnitude of a magnetic field within the waveguide becomes maximum in a position where the strip conductor pattern is inserted. Hence, a propagation mode of the microstrip line and a propagation mode of the waveguide are well coupled to each other. Accordingly, a high frequency signal which has been propagated through the waveguide can be propagated through the microstrip line without generating a large reflection (for example, refer to JP 2000-244212 A).
In such a conventional waveguide-to-microstrip transition as described above, about ¼ of the guide wavelength of the waveguide is required for a length from the strip conductor pattern to the shorting surface of the shorting waveguide block. Hence, the shorting waveguide block is projected from the dielectric substrate. Accordingly, there is a problem in that a transition is difficult to be miniaturized especially in a microwave band.
On the other hand, if a position shift occurs among the waveguide, then the shorting waveguide block, and the strip conductor pattern, characteristics of the transition are degraded. Thus, it is necessary to assemble the components or parts with high accuracy. However, there is a problem in that since the components or parts need to be made very small in the millimeter-wave band, the components or parts are difficult to be assembled with high accuracy, and hence mass production of the transition is difficult to be realized.
In addition, in the case where the conventional waveguide-to-microstrip transition is provided in an input/output portion of a package having high frequency elements mounted thereto, a space is made in a connection portion between the waveguide and the microstrip line. Thus, there is also a problem in that the inside of the package can not be hermetically sealed.
The present invention has been made in order to solve the above-mentioned problems, and it is therefore an object of the present invention to obtain a miniature waveguide-to-microstrip transition which is easy in mass production in a microwave band and a millimeter-wave band.
Moreover, it is another object of the present invention to obtain a waveguide-to-microstrip transition in which when the waveguide-to-microstrip transition is applied to a high frequency package having a waveguide connected at an input/output portion, the inside of the package can be hermetically sealed.